Federal Government had its sights set on expansion. There was an ideology that this "New World" that they had "discovered", claimed, and fought to make independent was destined to expand its boundaries. The only trouble was there were European power countries such as Spain and Great Britain that also wanted to stake a claim in to the newly discovered land and all of the resources it had to offer. The movement, letter tagged as "Manifest Destiny" was what drove American settlers to actively seek control of territories within the American continent and the Monroe Doctrine is what they later used to keep European nations from interfering with it. The Federal Government used manifest destiny to support expansion and believed the expansion was necessary to enforce the Monroe Doctrine. .
Manifest destiny was a phenomenon, a mindset, and a movement. It was never written in in stone or on paper. This was the idea that American Anglo-Saxons, or white Americans of English origin, were a superior race and destined to expand throughout the continent. Ideally, the intent was to set the boundaries of the continent from the Atlantic Ocean to the Pacific Ocean so acquiring lands west of the Mississippi River and southern territories were the main objective. Since these lands were inhabited by the Native Americans and the Mexicans, they would have to conform and accept the expansion, or literally be pushed aside. This mentality was used to run Native Americans off of their land, annex Texas, buy the north western territory of Mexico, and acquire the Oregon Territory.
One of the first obstacles of expansion was Native Americans. Andrew Jackson used the pressure of treaties to convince tribal leaders to relocate west of the Mississippi River. The idea was to have the natives conform to American society, end their tradition of hunting, and become farmers. Ultimately, the federal government hoped that by doing this, it would limit the amount of land needed by the natives, leaving more land for the American settlers to occupy.